gSMS
gSMS — Soil Moisture Sensor
The Medusa gamma Soil Moisture Sensor (gSMS) is a stationary gamma-ray spectrometer designed to measure soil moisture content over time. It is primarily used in agriculture to support irrigation decision-making.
The gSMS uses the same mDOS interface as all other Medusa detectors, with a few differences in measurement behaviour and data handling described in this chapter.
How the gSMS Works
The gSMS records data at a lower frequency than a mobile survey detector, suited to its stationary use case:
60-second interval — the spectrometer, GPS (optional), and PTH (optional) record at a 60-second interval. All data within each interval is summed (spectrometer) or averaged (GPS and PTH).
15-minute summation — fifteen consecutive 60-second spectral readings are summed and synchronised with a GPS and PTH reading. The summed record is analysed and radionuclide concentrations are derived.
3-hour upload — the 15-minute data is uploaded to the online Medusa portal at 3-hour intervals.
Measurement Range of the gSMS
Because the gSMS detector has a finite crystal size, both the crystal dimensions and the installation height determine the area from which gamma radiation can be measured. Radionuclides in the soil emit gamma rays uniformly in all directions, meaning the measurement area at the surface is circular, with the gSMS position at its center.
The measurement volume also extends into the soil. Directly beneath the detector, the measurement depth is greatest, while the effective depth decreases with increasing distance from the detector position.
The illustration below shows the effective measurement range of the gSMS both at the surface and within the soil. The indicated percentages represent the volume boundaries from which a given percentage of the measured signal originates. The accompanying table shows the radius of the surface area from which 95% of the measured signal originates for different installation heights.
Height of sensor (m) | Measurement radius (m) |
|---|---|
1 | 17.8 |
2 | 28.2 |
5 | 56.4 |
10 | 89.2 |
20 | 138.2 |
40 | 218.5 |
Installation
Just like any Medusa sensor, when power is connected, the sensor starts automatically.
Mount the sensor with the connector facing down to prevent moisture from entering through the PTH sensor opening. The sensor is supplied with mounting clamps that fit poles with a diameter of 50 mm.
Connecting to and accessing the mDOS interface works the same as for any other Medusa detector — see Connecting to the Detector.
Power Saving Mode
After 70 minutes, the gSMS enters a power saving mode: the LEDs, WiFi access point, and data uplink are turned off. Only data recording continues.
To access the interface after the sensor has entered power saving mode, either:
Connect via the wired Ethernet port, or
Power-cycle the sensor to restart it
Solar panel box (optional)
Optionally, the sensor system is supplied with a solar panel and charge controller, a waterproof enclosure for the controller and electronics, a battery, a metal battery cabinet, solar panel mounting clamps, and a 50 mm diameter pole for mounting the sensor at the desired height.
The figures below shows the inside of the metal cabinet where the battery is installed, together with the waterproof enclosure that houses the solar charge controller and electronics. The right figure shows the placement of the solar charge controller (blue module) inside the waterproof enclosure, including the electrical connections.
The two terminals on the left labeled “BATT” are used for the positive and negative battery connections. The two middle terminals labeled “PV” are connected to the positive and negative cables from the solar panel. The two terminals on the right labeled “LOAD” provide power output to the sensor.
The angled side of the metal cabinet is intended for mounting the solar panel.
Data Upload to the Portal
The gSMS uploads its 15-minute summed data to the Medusa portal at 3-hour intervals, starting at midnight GMT — uploads are attempted at 03:00, 06:00, 09:00, and so on. If a connection is established, all data on the sensor is uploaded. If no connection is available, data remains stored on the sensor until the next upload attempt.
When the sensor is powered and connected, a manual upload can be triggered from the Dashboard via the gSMS block.
Data can also be manually downloaded or deleted through the same gSMS block on the Dashboard.
The gSMS Portal
The gSMS portal is available at gsms.medusa-online.com. Access requires an account provided by Medusa, to which the detector is affiliated. The image below shows a screenshot of the data in the gSMS portal.
